---
title: "Secondary Dominants — AP Music Theory Definition & Guide"
description: "Secondary dominants are chromatic chords that act as V of a diatonic chord other than tonic, briefly tonicizing it. Essential for AP Music Theory Unit 7 analysis and part writing."
canonical: "https://fiveable.me/ap-music-theory/key-terms/secondary-dominants"
type: "key-term"
subject: "AP Music Theory"
unit: "Unit 7"
---

# Secondary Dominants — AP Music Theory Definition & Guide

## Definition

A secondary dominant is a chromatically altered chord that functions as the dominant (V or V7) of a diatonic chord other than the tonic, written with slash notation like V/V or V7/IV. It briefly tonicizes that chord, making it sound like a temporary tonic without actually changing keys.

## What It Is

A [secondary dominant](/ap-music-theory/unit-7/tonicization-through-secondary-dominant-chords/study-guide/rLCBduMA9EmMPYSSNiwd "fv-autolink") is a chord borrowed from outside the key that acts as the dominant of some chord *other than* the [tonic](/ap-music-theory/key-terms/tonic "fv-autolink"). In C major, the normal dominant is G (V). But you can also build a dominant for the G chord itself. That chord is D-F#-A, written **V/V** and read "five of five." The F# is the giveaway. It's not in C major, but it IS the leading tone in G major, so it pulls your ear toward G as if G were home for a moment.

That momentary pull is called **tonicization**. Here's the simplest way to think about it: a secondary dominant treats a [diatonic](/ap-music-theory/unit-1/major-keys-key-signatures/study-guide/fWrNAPRn7Np3XtWm1p4w "fv-autolink") chord like a guest of honor, giving it the same leading-tone-to-tonic resolution that V gives to I. You can build a secondary dominant for any major or minor diatonic chord (so V/ii, V/iii, V/IV, V/V, V/vi in major), but never for a diminished chord like vii°, because a diminished triad can't pose as a tonic. Spelling one is mechanical. Find the root a perfect fifth above the chord you're targeting, then build a major triad or dominant seventh on it, adding whatever accidentals that requires.

## Why It Matters

Secondary dominants are the centerpiece of [Unit 7](/ap-music-theory/unit-7 "fv-autolink") in [AP Music Theory](/ap-music-theory "fv-autolink"), the unit on secondary function. They're your first real step beyond purely diatonic harmony, and the exam treats them as core vocabulary rather than a bonus topic. You need them in three skill areas at once. In written analysis, you have to spot the chromatic accidental in a score and label the chord with correct slash notation. In part writing, you have to spell the chord and resolve its tendency tones correctly (the temporary leading tone resolves up, the chordal seventh resolves down). In aural skills, you have to recognize that brief "the music just leaned somewhere" moment in harmonic dictation. Secondary dominants also set up everything after them, since tonicization is the small-scale version of modulation, and understanding V/V makes full key changes much easier to hear and analyze.

## Connections

### Tonicization (Unit 7)

Tonicization is what a secondary dominant *does*. The secondary dominant is the [chord](/ap-music-theory/unit-3/triad-chord-qualities-m-m-d-a/study-guide/C2Wj35yXuDEj0tYdyQcc "fv-autolink"); tonicization is the effect of making a non-tonic chord sound like a temporary tonic for a beat or two. You can't explain one without the other on an FRQ.

### Functional Harmony (Units 4-5)

Secondary dominants only make sense if you already get [dominant function](/ap-music-theory/key-terms/dominant-function "fv-autolink"). V pulls to I because of the leading tone and the falling-fifth root motion. A secondary dominant copies that exact pull and aims it at a different chord. Same engine, new target.

### Diatonic Chord (Unit 4)

The target of a secondary dominant must be a diatonic chord in the home key (other than tonic, and not diminished). The [accidental](/ap-music-theory/key-terms/accidental "fv-autolink") in the secondary dominant is what makes it chromatic, which is exactly how you spot one in a score full of diatonic chords.

## On the AP Exam

Secondary dominants show up across both halves of the exam. In multiple choice, expect score-analysis stems asking you to identify a chord containing an accidental, where the correct answer uses slash notation like V7/IV, and aural questions where you identify a tonicization by ear. In the free-response section, the part-writing questions (realizing figured bass and realizing Roman numerals in four voices) regularly include secondary dominants, and graders check that you spelled the chromatic note correctly and resolved the temporary leading tone up by step. Harmonic dictation can also include a secondary dominant you have to notate and label. The most common point-loser is mislabeling V/V as a plain II chord. If you see a major-quality chord built on re with a raised fa, it's functioning as a dominant, so label it that way.

## Secondary Dominants vs Modulation

Both involve a new accidental and a pull toward a new tonal center, but they differ in scale. A secondary dominant tonicizes a chord for a moment, then the music continues in the original key, so you keep analyzing in the home key with slash notation. Modulation actually changes keys, establishing a new tonic with its own cadence, so your Roman numeral analysis switches to the new key. Quick test: if the new tonal center gets confirmed by a cadence and sticks around, it's a modulation; if it's gone in a chord or two, it was just a secondary dominant doing its job.

## Key Takeaways

- A secondary dominant is the dominant of a diatonic chord other than tonic, written with slash notation such as V/V or V7/IV.
- To spell one, find the root a perfect fifth above the chord being tonicized, then build a major triad or dominant seventh chord, adding accidentals as needed.
- The chromatic accidental in a secondary dominant is the temporary leading tone of the tonicized chord, and it must resolve up by step.
- You can tonicize any major or minor diatonic chord, but not a diminished chord like vii°, because a diminished triad can't function as a tonic.
- A secondary dominant creates a brief tonicization, not a modulation, so you keep analyzing in the original key.
- If a chordal seventh is present (as in V7/V), it resolves down by step, just like the seventh in a regular V7 chord.

## FAQs

### What is a secondary dominant in AP Music Theory?

A secondary dominant is a chord that functions as the dominant (V or V7) of a diatonic chord other than the tonic, labeled with slash notation like V/V. In C major, V/V is a D major chord (D-F#-A) that pulls toward G the way V pulls toward I.

### Is a secondary dominant the same as a modulation?

No. A secondary dominant tonicizes another chord for only a moment, and the music stays in the home key, so you keep your Roman numeral analysis in the original key. A modulation is a true key change confirmed by a cadence in the new key.

### What's the difference between a secondary dominant and tonicization?

The secondary dominant is the chord itself; tonicization is the effect it creates. When V7/IV resolves to IV, the chord is the secondary dominant and the brief moment where IV sounds like tonic is the tonicization.

### Can you have a secondary dominant of vii°?

No. Diminished chords can't be tonicized because a diminished triad can't sound like a stable tonic. In a major key, your options are V/ii, V/iii, V/IV, V/V, and V/vi (V/IV requires adding the seventh, since V/IV without it is just the tonic triad).

### How do I identify a secondary dominant in a score on the AP exam?

Look for an accidental that isn't in the key signature, then check whether the chord is a major triad or dominant seventh resolving down a fifth (or up a fourth) to a diatonic chord. If so, label it with slash notation, like V7/vi, instead of a plain chromatic Roman numeral.

## Related Study Guides

- [7.2 Part Writing of Secondary Dominant Chords](/ap-music-theory/unit-7/part-writing-secondary-dominant-chords/study-guide/S2WJUDMF6J2GBqPvLiGg)

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